New study paves the way for quantum-enhanced computation

Despite the widespread research in quantum computers, no-one has built a machine that uses quantum-mechanics to solve computational problems faster than a classical computer.

Quantum computers harness the power of atoms and molecules to perform memory and processing tasks and have the potential to perform certain calculations significantly faster than any silicon-based computer.

Now scientists from the Universities of Southampton and Oxford have worked together to develop the first experimental demonstration of the boson sampling model of computation, which could pave the way to larger devices that could offer the first definitive quantum-enhanced computation. Boson sampling, by taking advantage of recent advances in photonics, offers a promising route to building such a device in the not-distant future, providing convincing evidence for the computational power of quantum mechanics.

Photons are absolutely identical at a fundamental level – formally they are bosons – which means that they exhibit strong quantum level – ‘entanglement ’. This means that if two sufficiently identical photons come together they behave in a connected way – almost as if they ‘clump’ together. When scaled up to multiple input photons these ‘entanglements’ cause the outputs of a boson-sampling circuit to ‘clump’ together in a characteristic way, predictable by quantum mechanics, but difficult to calculate using conventional computers.

The University of Southampton team, led by Professor Peter Smith and Dr James Gates from the Optoelectronics Research Centre (ORC), developed the photonic chip on which the experiment was performed. Dr Gates says: “The chip offers a scalable route, perhaps the only scalable route, to build large linear systems required for larger boson sampling machines. If one is going to eventually need to move ‘on chip’ with more complex boson sampling machines, there is obvious benefit in building the proof-of-principle devices ‘on chip’ as well. The move to optical processing on a chip format can be likened to the shift to integrated silicon chips in electronics.”

The work is part of a long term collaboration with Professor Ian Walmsley’s group at the Clarendon Lab, University of Oxford. Supported by the Engineering and Physical Sciences Research Council (EPSRC), this latest output involved fabrication and optical characterisation at the University of Southampton and the quantum measurements being made in Oxford. Lead author Justin Spring from the University of Oxford describes the significance as: